Branched stent/graft and method of fabrication

ABSTRACT

Branched braided stent or graft devices and processes for fabrication of the devices are disclosed in which a trunk portion and two hinge leg portions are fabricated in one piece braided from a single plurality of filaments, whereby the legs contain the full plurality of filaments and the trunk portion contains a subset of the same plurality of filaments. The fabrication process involves braiding the hinged legs on a mandrel while retaining loops of filament between the hinged leg portions for subsequent braiding of the trunk portion of the stent or graft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/823,430, filed Jun. 27, 2007, which is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present development relates generally to stent or graft devices forimplantation in an anatomical structure and, more particularly, tointravascular catheter deliverable branched stent or graft devices andmethods of fabrication. Embodiments include unique branched stent orgraft devices for the treatment of abdominal aortic aneurysms (AAA)involving the aorta-iliac bifurcation by reinforcing, excluding,bridging, or lining the diseased vessel, and to methods of fabricationof such as stent or graft devices involving a unique braiding techniqueusing a single plurality of filaments to form two hinged legs and thecommon body or trunk portion of the device.

II. Related Art

An aortic aneurysm is a weak area in the wall of the aorta, the mainblood vessel that carries blood from the heart to the rest of the body.The aorta extends upwards from the heart in the chest and then archesdownwards, traveling through the chest (the thoracic aorta) and into theabdomen (the abdominal aorta). The normal diameter of the abdominalaorta is about one inch (2.5 cm).

Aortic aneurysms are frequently caused by the breakdown of the muscularlayer and the elastic fibers within the wall of the aorta. The breakdownusually occurs over time, frequently in patients over 40 years of age,and can be caused by prolonged high blood pressure, effects from smokingor a genetic predisposition. As the vessel tissues deteriorate, thevessel wall strength decreases, and the high blood pressure causes theaortic wall to stretch beyond its normal size, forming an aneurysm. Theweak aneurysm bulges like a balloon over time and can burst if the wallbecomes too thin and weak to hold the blood pressure.

Most commonly, aortic aneurysms occur in the portion of the vessel belowthe renal artery origins. The aneurysm may extend into the aorta-iliacbifurcation and into the iliac arteries supplying the hips, pelvis andlegs.

Once an aneurysm reaches 5 cm (about 2 in.) in diameter, it is usuallyconsidered necessary to treat to prevent rupture. Below 5 cm, the riskof the aneurysm rupturing is lower than the risk of conventional surgeryin patients with normal surgical risks. The goal of therapy foraneurysms is to prevent them from rupturing. Once an AAA has ruptured,the chances of survival are low, with 80-90 percent of all rupturedaneurysms resulting in death. These deaths can be avoided if theaneurysm is detected and treated before it ruptures and ideally treatedat an early stage (smaller aneurysm) with a lower risk procedure.

AAA can be diagnosed from their symptoms when they occur, but this isoften too late. They are usually found on routine physical examination,through use of ultrasound, or by chest and abdominal X-rays. Onexamination, a doctor may feel a pulsating mass in the abdomen. If thedoctor suspects an aneurysm, he/she will probably request that anultrasound scan be carried out. Other scans, such as computerizedtomography (CT) and magnetic resonance imaging (MRI) may also beperformed. These scanning techniques are very useful for determining theexact position of the aneurysm.

The surgical procedure for treating AAA involves replacing the affectedportion of the aorta with a synthetic graft, usually comprising a tubemade out of an elastic material with properties very similar to that ofa normal, healthy aorta. This major operation is usually quitesuccessful with a mortality of between 2 and 5 percent. The risk ofdeath from a ruptured AAA is about 50%, even during surgery.

More recently, instead of performing open surgery in undertakinganeurysm repair, vascular surgeons have installed an endovascularstent/graft delivered to the site of the aneurysm using elongatedcatheters that are threaded through the patient's blood vessels.Typically, the surgeon will make a small incision in the patient's groinarea and then insert a delivery catheter containing a collapsed,self-expanding or balloon-expandable stent/graft to a location bridgingthe aneurysm, at which point the stent/graft is delivered out from thedistal end of the delivery catheter and allowed or made to expand toapproximately the normal diameter of the aorta at that location. Thestent/graft, of course, is a tubular structure allowing blood flowthrough the lumen thereof and removing pressure from the aneurysm. Overtime, the stent/graft becomes endothelialized and the space between theouter wall of the stent and the aneurysm ultimate fills with clottedblood. At this time, the aneurysm is no longer subjected to aorticpressures and thus will not continue to grow.

In treating AAAs that involve the aorta-iliac bifurcation, various stentor grafts designs have been placed to support, bridge or reline thevessels in the aneurysm segments. This has often involved multiple selfexpanding stents or stent grafts such as a large diameter stent or graftin the aortic segment and two smaller stents or grafts placed in each ofthe iliac arteries. In other designs the stent or graft has beendesigned to extend from the aortic segment into one branch of the iliacartery. In this case a hole is provided in the stent or graft toaccommodate blood flow to the other iliac artery. A second stent orgraft may be optionally placed into the other iliac artery and extendinginto the hole in the first stent or graft provided for iliac branchblood flow.

It has become apparent through use and clinical experience that thejunctions of multiple stents or grafts presented placement problems ofcomponent alignment within the body. The stents or grafts beingindependent of each other caused components to rub against each othercausing metal fatigue and flow discontinuities or thrombosis could occurwhere one component was not aligned with another and protruded into theblood flow. Use of multiple components also caused uneven vessel supportsuch as where overlapping components may have an excess in vesselsupport as well as unsupported portions of the vessel where gaps occurbetween components. In the case of grafts, gaps between components causeleaks and may result in continued blood pressure exposure to theaneurysm.

As a result there remains a need for an alternative one piece stent orgraft designs that covers the entire aneurysm segments including themain aortic segment as well as both iliac artery segments. It is alsodesirable that such a design be collapsible for percutaneous catheterdelivery to the treatment site as well as self expandable when deployedfrom the delivery catheter.

U.S. Pat. No. 6,409,750 to Hyodoh et al. discloses woven bifurcated andtrifurcated stents together with methods of fabrication. Those devicesinclude a first plurality of wires defining a first leg having a firstportion and a second plurality of wires defining a second leg having asecond distal portion, and a common body having a distal end and aproximal portion, the common body being formed from at least the firstand second plurality of wires, the proximal portion of the common bodybeing adjacent to the distal portions of both legs, and both ends of atleast one wire from both of the pluralities being located proximate thedistal end of the common body. In this design the braided legs areconnected only by the common body portion and gaps in metal coverageoccur near the juncture of the legs.

U.S. Pat. No. 7,004,967 to Chouinard et al. describes a process formanufacturing a braided bifurcated stent. The process involves the useof two or more braiding machines in which a first discrete plurality offilaments are braided to form a first leg, and a second discreteplurality of filaments are braided to form a second leg. The processinvolves braiding the first plurality of filaments and the secondplurality of filaments together to form the body using another braidingmachine. That design results in metal coverage gaps occurring at theoutside top portion of each leg and the process requires the use ofmultiple braiding machines. As with other concepts, the legs are notconnected except to the common body portion. There are no common wiresfrom one leg connecting to the other leg so a gap occurs between them.

There exists a need for a one piece branched stent or graft device thathas improved metal coverage for uniform properties and a manufacturingprocess that is simple and produces a one piece design from a singlediscrete plurality of wires. There is a need for an improved bifurcatedstent or graft that incorporates wires from one leg into the other legcreating a wire hinge and reinforcing the crotch area of the device.There is also a need for a device having the improved characteristics asabove and which is also deliverable using a percutaneous intravascularcatheter approach having a collapsed configuration for delivery througha catheter and a self expanding configuration when released from thecatheter confines. The present development provides such a device.

SUMMARY OF THE INVENTION

The present concept includes embodiments of catheter-deliverable,endovascular, one piece, multi-region stent or graft devices.Embodiments include bifurcated stent or graft devices for treatingabdominal aortic aneurysms involving the aorta-iliac bifurcation. Animportant aspect of the concept includes a braiding fabricationtechnique that enables a single bundle or a single plurality offilaments to be used to form a plurality of regions, such as distinctregions of a device including a first region, a second region and athird region.

One preferred embodiment, for example, includes three regions: the firstregion and second region form two hinged legs and a third region forms acommon body or trunk portion of the device. The third region is braidedfrom a subset of the same single plurality of filaments forming the twohinged legs. In this manner, the stent or graft structure includes asingle plurality of resilient filaments that are braided to define apair of hinged legs and a common body or trunk. The stent or graft has afilament hinge in the crotch area connecting the legs. The filaments arepreferably a shape memory metal such as nitinol wire but may be or mayinclude other metals that have an elastic heat settable shape. A polymerfilament overlaying version can be used as part of a grafted device.

As used herein the terms “filament” and “wire” are used interchangeablyto describe strands of any suitable type of material including metal andnon-metal materials used in aspects of the devices. As used herein, theterm “braiding” includes interweaving where appropriate. It will beappreciated the term includes any braid or weave which enableselongation of the device with corresponding reduction in diameter sothat the device may be delivered by vascular catheter.

One preferred method of fabrication includes braiding a plurality ofhighly elastic filaments supplied from a plurality of braiding spoolsonto an assembled two-piece or two-part mandrel. The filaments arebraided onto a first part of the mandrel to form a first leg. Thebraiding is stopped and the braid is secured around the mandrel at thefirst leg distal end (last braided portion) using tape or other clampingmeans.

Long loops are formed from each filament exiting the tape/clamp abovethe distal end of the leg except for filaments that are intended to bethe crotch or hinge filaments or wires connecting the legs. The filamentloops created are made long enough to later be braided into the commonbody portion or trunk of the stent or graft. Once the loops are formed,they are coiled or spooled and secured to be out of the way so as not tobecome entangled in continued braiding. The loop end is taped/clamped tothe mandrel on top of the loop starting point. The braiding process isrestarted and a second leg is braided over a second part of the mandrelusing the same plurality of filaments that were used to braid the firstleg.

Once the second leg has been braided to a desired length, the filamentsare taped/clamped to the mandrel and cut from the braiding spools. Thebraid and mandrel are removed from the braiding machine. The two partsof the two-piece assembled mandrel are separated and the legs and firstand second mandrel parts are manipulated in relation to each other toposition the legs adjacent each other connected by the hinge filaments.Next, a common body portion or trunk mandrel is attached using legextensions designed to be inserted into the top of each leg mandrel. Theloops that were formed and coiled or spooled are then made available forbraiding the common body portion or trunk of the stent/graft.

At this point, a plurality of trunk braiding options are available and adecision is now required to determine which variation of braiding thetrunk is to be selected. One option or choice is to leave the spooledloops intact and braid both filaments of each loop along the same path.A second choice is to unwind the loops, sever the end of each loop andrewind the two filaments onto separate braiding spools. The two braidedloop filaments can then be wound in opposite helical directions.

In either braiding choice the filaments are spooled and placed on thebraiding machine spool carriers and the new mandrel assembly isinstalled in the braiding machine. The common body portion or trunk isthen braided using a major portion of the same plurality of filamentsused to braid the legs. The remaining portion of the plurality offilaments or those not used to braid the trunk, are the filamentsselected to form the hinge connecting the legs. The braiding machine forbraiding the trunk will require a different number of spool carriers ascompared to the leg braiding. In the case of the loops being severedinto two pieces, for example, the number of braiding machine spoolcarriers will be much higher in number than if the loops are leftintact.

Aspects of the inventive concept encompass both the method offabrication of the branched stent or graft device and also the medicaldevice that results from use of the process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the braiding of both legs of abranched stent or graft device over an assembled two-part mandrel andshowing the formation of loops between the leg segments;

FIG. 2 is side view of two legs of the device of FIG. 1 after braidingand separation of the two-piece mandrel;

FIG. 3 is a top view of the device shown in FIG. 2 illustrating thefilaments available for braiding the trunk portion of the device;

FIG. 4 is a perspective drawing of a trunk mandrel prior to assembly tothe leg mandrels;

FIG. 5 is a top view of the legs indicating an area for optional manualbraiding;

FIG. 6 is a side view of one embodiment of a final device;

FIG. 7 is a side view of an alternative embodiment; and

FIG. 8 is a schematic top view illustrating a 32 filament braidershowing the spool carriers 1-32.

DETAILED DESCRIPTION

Embodiments will next be described with reference to the drawingfigures. Such figures and the accompanying detailed description aremeant to be illustrative rather than limiting and are included tofacilitate the explanation of aspects of the inventive concepts,including devices and methods of fabrication of the devices.

Two preferred final device configurations of a branched stent/graft areshown in FIGS. 6 & 7. These embodiments consist of two leg portionsformed with a common body or trunk portion.

One aspect of the development involves the materials of construction ofa device contemplated by the present invention. The device is fabricatedfrom a single plurality of filaments which in the preferred embodimentshould include a material which is both resilient and which can be heattreated to substantially set a desired shape. Materials found suitablefor this purpose include a cobalt-based low thermal expansion alloyreferred to in the field as Elgeloy, nickel-based high temperaturehigh-strength “superalloys” commercially available from HaynesInternational under the trade name Hastelloy, nickel-based heattreatable alloys sold under the name Incoloy by International Nickel,and a number of different grades of stainless steel. The importantfactor in choosing a suitable material for the filaments or wires isthat the filaments retain a suitable amount of the deformation inducedby a molding surface when they are subjected to a predetermined heattreatment.

One class of materials which also meet these qualifications includesso-called shape memory alloys such as nitinol, an approximatelystoichiometric alloy of nickel and titanium, which may also includeminor amounts of other metals to achieve desired properties. Such alloystend to have a temperature induced phase change which will cause thematerial to have a preferred configuration which can be fixed by heatingthe material above a certain transition temperature to induce a changein the phase of the material. When the alloy is cooled back down, thealloy will “remember” the shape it was in during the heat treatment andwill tend to assume that configuration unless constrained from so doing.

As an example, without limitation, the device can be illustrated beingfabricated from 32 braided nitinol wires having a diameter ranging from0.0015-0.008 inch (0.0381-0.203 mm), preferably 0.002-0.005 inch(0.051-0.127 mm). The number of wires to be braided may range from 4-200or more, preferably from 8 to 144 and, more preferably, from 16-72depending on the particular device characteristics desired. FIG. 8 showsa schematic top view illustrating 32 numbered spool carriers on abraiding machine 100. All the even numbered spool carriers travel in onedirection (clockwise) and all the odd numbered spool carriers travel inthe opposite direction (counter-clockwise). In addition, as the spoolcarriers travel in a circular direction, they also change radius oftravel about the center of the braider passing inside of one spoolcarrier and outside of the next spool carrier, thereby forming wireswrapped about a center mandrel that are woven over and under each otherin a braided configuration. As the spool carriers are moving, themandrel is slowly moved in a vertical direction at a controlled speedrelative to the braider speed to set the pitch of the braided wires. Atypical pitch angle may range from 30-70 degrees from the longitudinalaxis of the braided tube in the, as braided, relaxed tube prior to heattreatment. The pitch, pick count (number of wire crossovers per inch, orother lineal measure) and wire diameter, are all variables that can bealtered to change the device characteristics as well as the heat setshape.

Referring now to FIG. 1, there is shown a tubular mandrel consisting oftwo parts 20 and 22. The two-piece mandrel may be assembled together bysliding the two parts over a close fitting shaft and holding them inplace with removable end caps (not shown) or by any number of otherknown suitable means. The braiding of a first region or leg 24 begins atthe bottom of the mandrel as indicated in the illustration. The braidstarts by attaching, as by taping or clamping, the thirty-two filamentsor wires 25 to the mandrel as at 26. The braiding is begun at acontrolled pitch until a desired sufficient length is generated for thefirst leg 24 near the center of the assembled mandrel The braiding isstopped and the braided wires are next taped or clamped in place on themandrel at location 28.

After the braiding of the first leg 24, a hinge zone 30 that representsthe portion of the circumference of the first braided leg 24 to beconnected directly to the second braided leg 36 is designated. In apreferred arrangement using the illustration of a thirty-two filament orwire braid, this will typically range between about 4 to 8 wires or from4/32 to 8/32 (⅛ to ¼ of the total) of the circumference of the legsbased on the thirty-two filament braid. As an example, 4 wires may bedesignated as the hinge area 30. That leaves (32−4) or 28 remainingwires of the braid that will be configured differently.

Each of the remaining 28 wires leading from the spool carriers as at 32will have a specific length of filament or wire drawn off the spool toform a loop as at 34 of wire, the loop beginning at the taped mandrel at28 (end of leg one) and ending back at the same spot at the mandrel. Theloop length is predetermined and is at least the length needed to braidthe common body portion plus leader length for a braiding machine. Theloops 34 are taped to the mandrel over the first tape at location 28such that the wire leading back to the spool carrier as at 32 is at thesame position as it was prior to the forming of the loop. After eachloop 34 is secured, the loop material may be spooled or otherwise routedaway from the braiding action to prevent the filament or wire frombecoming entangled with the next braiding process.

It will be appreciated that all 32 wires are still oriented radiallyabout the mandrel to begin braiding the second leg 36 from tapedfilaments as also shown in FIG. 1. The braiding is started at about midpoint on the assembled mandrel and continues until the desired braidedlength for the second leg 36 has been completed. At this point, bothends of the leg 36 braid are secured to the mandrel by tape 38 and 40(FIG. 2) or other clamping means. Next, the 32 wires from the spoolcarriers may be cut about 2 inches (5.1 cm) from the mandrel and theassembled mandrel and braided legs may be removed from the braidingmachine along with the 28 loops of braid filament or wire. A typicalfilament feed spool is shown at 44 mounted on a spool carrier device 42in a well known manner.

In FIG. 2, the central shaft of the mandrel has been removed so that thetwo halves of the mandrel may be separated and manipulated relative toeach other to assume the relative positioning shown in the Figure. Forexample, the upper mandrel for the second leg may be turned upside downand pivoted about the hinge 30 as shown. The wire loops 34 are shown inthe top view in FIG. 3. Note that the hinge area 30 has no loops as nonewere formed in this region.

As indicated, there are several options involving different proceduresfor forming the body or trunk portion of the device. Versions ofpreferred embodiments and examples will be discussed next.

In a first embodiment, the distal ends of the wire loops are not cut orsevered and each of the loops 34 is wound with the two wires togetheronto a spool for braiding the common body or trunk of the stent/graftusing double strands. Thus, in the example, 28 spools of two filamentsor wires each are available to be placed onto a braider that has atleast 28 spool carriers.

In an alternate embodiment, the wire loops are severed toward the endsto form two wires of substantially equal length from each original loop.The two wires are wound on separate spools for placement on a braiderincluding at least (2 times 28) or 56 spool carriers.

FIG. 4 illustrates one shape of a mandrel at 50, which may be solid orhollow, for forming the common body or trunk of the stent or graft.There are two pilot diameters or leg extensions 52 and 54 for insertioninto the corresponding two-leg mandrels. The now three-part mandrel issecured together by fasteners or other known means and mounted into thebraider in a well known manner for braiding the third region or commonbody or trunk configuration of the device. The corresponding spools areloaded onto the spool carriers as well.

FIG. 5 illustrates an area of transition between the stent/graft legdiameter and the trunk diameter where it may be advisable to optionallyhand braid about 4-8 wires of each side of the device as at 60 and 62 tobridge the diameter transition prior to beginning of the machinebraiding for the trunk. To do this, the spools involved in the handbraiding are removed from the carrier and then returned to the carrierprior to full machine braiding. This optional process provides smalleropenings in the stent/graft between wires in the leg to crotch to trunktransition and makes for a less open device lattice.

As indicated in one embodiment, the 28 pairs of wires are braidedtogether over the mandrel in FIG. 4 for the desired length of the trunk.The braiding is stopped and the filaments or wires are taped or clampedto the mandrel. The wires leading to the spools are cut and the mandrelassembly and braided device are removed from the braider. A finisheddevice in accordance with the embodiment is shown in FIG. 6. The trunkportion with the mesh of double filament loops is shown at 72.

In an alternative embodiment, the severed loops on 56 individual spoolsof wire are braided together over the trunk mandrel 50 in FIG. 4 for thelength of the trunk shown in the embodiment 80 in FIG. 7 as 82. Thebraiding is then stopped and the wires are taped or clamped to themandrel. The wires leading to the spools are cut and the mandrelassembly and braided device are removed from the braider. The finisheddevice 80 has a trunk portion braided from single filaments or wires asis shown in FIG. 7.

In the embodiment with the loop braid, the final braiding of the trunkmay be accomplished on the same original 32 carrier braider used forbraiding the legs, but four of the spools, i.e., every 8th spool, wouldbe empty. However, this would cause the final device to exhibit gapsbetween some of the braided wires. This is not as desirable as using abraider with the exact number of needed spool carriers. The gaps can bemanually spaced more evenly prior to the final device heat treatment tobe discussed in the following. Braiders are available in a wide varietyof spool carrier numbers such as 4-200 or more in increments of fourcarriers as offered, for example, by Steeger USA, Spartanburg, S.C.

The heat treatment process follows the braiding of the device. In thecase where the braiding process was accomplished on a mandrel thatequals the final device size, the braid may remain on the mandrel if themandrel was made of metal or a material able to adequately handle thetemperature of the device heat treatment. Heat treatment techniques aregenerally known to those skilled in the art.

U.S. Pat. No. 5,725,552 to Kotula et al., incorporated herein inentirety by reference, for example, describes in great detail the heattreatment of braided medical devices made of nitinol wire and theprocess of confining the device in a mold of the desired final deviceshape during the heat treatment to set the final device shape in memory.In this regard, it has been found that holding a nitinol fabric or braidat 500-550° C. for a period of about 1-30 minutes, depending on thehardness or softness desired, will tend to set the braid in the shapeheld during the heat treatment. The materials used to hold the braid inplace must be suitable for the temperature range of the heat treatment.For example, the tape if used to hold the braid down may not besuitable, so a metal clamp may be substituted or other means known inthe art.

The devices shown in FIGS. 6 & 7 show a slight amount of flare at thetrunk as at 74 and 84 and the leg ends as at 76 and 78 (FIG. 6) whichcan be molded in during a heat set process by holding the braid in theflared condition during the heat set. Any gaps between wires, such asoccurring from braiding 28 wires on a 32 spool carrier braiding machinemay also be manually repositioned as desired. After heat treatment, theywill retain the repositioned shape.

If the braiding mandrel is not the desired final heat set shape for thedevice, the braided device may be removed from the mandrel and placed ina separate mold to produce the desired shape for heat treatment. Afterheat treatment and shape setting, the braid will resist unravelingwithout the need for clamps or other retention means. The flared ends ofthe trunk and legs have been found to assist the device in seatingagainst the artery walls and, in addition, help prevent the wires fromcatching on other devices that may be passed through the stent or graft.Preferably, the trunk and legs are sized to be somewhat larger (example5-30%, preferably 15-20%) in the stent/graft relaxed state than the sizeof the artery in which they are to be placed, to thereby exert outwardpressure on the arterial wall to aid in device seating and retention.

Heat set stents or grafts fabricated by the present braiding process areeasily collapsed to a small diameter for delivery through anintravascular catheter lumen by pulling on the trunk and leg ends andstretching the braided wires along the longitudinal axis of the device.Once the device is positioned within the catheter and delivered to thetreatment site, the stent/graft may be urged out of a catheter lumen endopening. The released device will self expand to its heat set memorizedsize or against the arterial wall if the artery is smaller. It will beappreciated that the design of the delivery catheter is somewhat morecomplex for a branched stent or graft. Examples of such delivery devicesare illustrated in detail in U.S. Pat. No. 6,409,750 to Hyodoh et al.and U.S. Pat. No. 6,953,475 to Shaolian et al.

The branched braided configuration may be used as a stand alone stent orthe braid may be a component of a graft whereby a polyester or otherbraided polymer or woven fabric may be added to the outside of thebraided metal structure to serve as a sealing surface to the graft. Inthis type of configuration, the braided metal expansion characteristicsurge the graft fabric out against the arterial wall. The fabric may beattached to the braid by suture as an example or by other means known inthe graft art. Alternatively, the polyester or other braided polymer orwoven fabric may be added to the inside of the braided metal structureand attached by suture.

Another embodiment of the graft consists of braiding a separatepolyester filament using the same techniques as described for the metalfilaments or wires. In this embodiment, the braided polymer branchedgraft material is placed over the heat set metal braid structure and thepolymer braid sutured to the metal braid for retention. Alternatively,the branched graft material may be placed within the metal braidedstructure and sutured to the metal structure. By using similar pitch andpick count for both the metal braid and polymer braid the device caneasily collapse and self expand as a unitary device. It should be notedthat the underlaying or overlaying polyester or other braided polymermay be fabricated of multiple independent components attached to themetal structure.

In still another embodiment the graft is made using the same braidingprocess but the single plurality of filaments used to fabricate thegraft consists of a combination of metal and polymer filaments braidedtogether in a single operation. The number of metal and polymerfilaments and the ratio of metal to polymer may be altered as desired toobtain sufficient self expansion force and adequate polymer density forsealing of the graft. The process allows for a great deal of flexibilityin graft design.

The present stent or graft braiding process, unlike other techniques,provides for fabrication of a one piece tubular framework device wherebythe legs are connected by a hinge and the legs and trunk are fabricatedfrom a single plurality or array of filaments. It will be appreciatedthat the legs may be the same or unequal in length, the same or unequalin diameter and of a constant (uniform) or vary in diameter along thelength thereof (longitudinal axis) as desired in a particularapplication.

Although the example device illustrated is for the treatment of anabdominal aortic aneurysm involving the iliac bifurcation, it will beappreciated that the process for braiding and the resulting device ismore broadly applicable and not limited to a branched stent or branchedgraft and a process for fabricating a branched stent or graft fortreating a particular condition. There are numerous locations within thebody where such a branched stent or graft may be needed and the processis suitable for other configurations as well as the inverted Y stent orgraft illustrated. For example, it is anticipated that a side branch canbe fabricated off a main braided tubular body in the manner of thisinvention by creating loops of filaments in a circular pattern at thelocation of the intended side branch. Such a process involves stoppingthe braiding machine as braid wires cross the side branch location,creating the loops, and repeating the process until the branch take offarea is passed by the braiding. Once the main tube is braided, the loopsmay be used to braid the side branch.

This invention has been described herein in considerable detail in orderto comply with the patent statutes and to provide those skilled in theart with the information needed to apply the novel principles and toconstruct and use embodiments of the example as required. However, it isto be understood that the invention can be carried out by specificallydifferent devices and that various modifications can be accomplishedwithout departing from the scope of the invention itself.

1. A method of fabricating a braided device suitable for implantation inan anatomical structure, the braided device having a first leg, a secondleg, a common body coupled to the first leg and the second leg, and ahinge between the first leg and the second leg, the method comprising:(a) braiding a single discreet plurality of filaments to form the firstleg on a portion of a first tubular mandrel; (b) designating a number ofsaid discreet plurality of filaments as a hinge zone to connect directlyto a second leg and forming extended loops from the remainder of saidfilaments; (c) braiding said first discreet plurality of filaments toform a second leg about a second portion of said first tubular mandrel;and (d) braiding the portions of the filaments formed into extendedloops on a second tubular mandrel to form a common body attached to thefirst and second legs.
 2. The method of claim 1, wherein said firsttubular mandrel is a two-piece mandrel assembled from two temporarilyjoined mandrel parts, wherein each leg of the braided device is braidedon a separate part of the first tubular mandrel, and further comprisingseparating the two joined mandrel parts after said second leg isbraided, the mandrel parts remaining connected by said hinge zone, andattaching both mandrel parts to said second tubular mandrel prior tobraiding said common body.
 3. The method of claim 1, wherein saidplurality of filaments comprise a shape memory alloy and furthercomprising heat treating said braided device to set the shape of saiddevice after braiding is completed.
 4. The method of claim 3, furthercomprising conforming the braided device to the shape of a mold for theheat treatment step.
 5. The method of claim 3, further comprisingcreating a second braided device, the second braided device comprisingnon-metallic filaments, and placing the second braided device adjacentto the braided device comprising the shape memory alloy to form acomposite graft device.
 6. The method of claim 5, further comprisingsecuring said devices together.
 7. The method of claim 1, furthercomprising securing said loops to prevent them from being entangledduring the braiding of said second leg.
 8. The method of claim 1,wherein each of said loops is severed prior to the braiding of thecommon body.
 9. The method of claim 1, further comprising flaring theouter ends of the braided device.
 10. The method of claim 1, whereinsaid braiding steps include machine braiding.
 11. The method of claim 1,wherein said hinge zone comprises from about ⅛ to about ¼ of saiddiscreet plurality of filaments.
 12. The method of claim 1, furthercomprising hand braiding a portion of the filaments located on each sideof said hinge zone prior to braiding said common body.
 13. The method ofclaim 1, further comprising securing the braided strands of the firstleg to the first tubular mandrel prior to forming the extended loops.14. The method of claim 1, further comprising securing the extendedloops to the first tubular mandrel prior to braiding the second leg. 15.A method of fabricating a braided device suitable for implantation in ananatomical structure, the braided device having a first leg, a secondleg, a common body coupled to the first leg and the second leg, and ahinge between the first leg and the second leg, the method comprising:(a) braiding a plurality of filaments from a first location to a secondlocation on a mandrel to form the first leg; (b) selecting a subset ofthe plurality of filaments to form the hinge, each of the subset offilaments having a free end available for continued braiding; (c)forming a loop in each of the remaining filaments of the plurality offilaments to form filament loops, each loop beginning and endingproximal to the second location on the mandrel, each filament bearing aloop having a free end available for continued braiding; (d) braidingthe free ends of the plurality of filaments, including both the hingefilaments and the filaments bearing loops, on a mandrel to form thesecond leg; and (e) braiding either the filament loops, or wires formedby severing the filament loops, on a mandrel to form the common body ofthe braided device.
 16. The method of claim 15, wherein the first legand the second leg are braided on a tubular mandrel comprising a firstsegment and a detachable second segment axially aligned with the firstsegment.
 17. The method of claim 15, wherein the subset of filamentsselected for the hinge represents about ⅛ to about ¼ of the plurality offilaments.
 18. The method of claim 15, wherein the number of filamentsin said plurality of filaments is from about 4 to about
 200. 19. Themethod of claim 18, wherein the number of filaments in said plurality offilaments is from about 8 to about
 144. 20. The method of claim 19,wherein the number of filaments in said plurality of filaments is fromabout 16 to about
 72. 21. The method of claim 15, wherein the pluralityof filaments consists of about 32 filaments and the number of filamentsforming the hinge is from about 4 to about 8 filaments.
 22. The methodof claim 15, wherein the plurality of filaments are constructed of ashape memory metal, and the method further comprises the step of heattreating the braided device to set the braided device into a desiredfinal shape.
 23. The method of claim 22, wherein the shape memory metalis nitinol.
 24. The method of claim 22, wherein the heat treating stepcomprising heat treating the braided device such that one or more endsof the braided device are flared.
 25. The method of claim 15, whereinthe plurality of filaments of the braided device are metallic filamentsand further comprising the step of placing a non-metallic braided layeradjacent to the braided device to form a composite graft device.
 26. Themethod of claim 15, wherein the braided device is a metallic braideddevice comprising metallic filaments and further comprising the stepsof: repeating the steps of (a) through (e) with a plurality ofnon-metallic filaments to form a non-metallic braided device, andplacing the non-metallic braided device adjacent to the metallic braideddevice to form a composite graft device.
 27. The method of claim 26,wherein the metallic braided device and the non-metallic braided deviceare braided using a similar pitch and pick count.
 28. The method ofclaim 15, wherein the plurality of filaments of the braided device are acombination of metallic and non-metallic filaments.
 29. The method ofclaim 15, wherein the pitch angle of the braided device ranges fromabout 30 to about 70 degrees from the longitudinal axis of each of thefirst and second legs and the common body.
 30. The method of claim 15,wherein step (e) comprises braiding the filament loops to form thecommon body.
 31. The method of claim 15, wherein step (e) comprisessevering the filament loops into two severed wires, and braiding thesevered wires to form the common body.
 32. The method of claim 15,further comprising securing the braided strands of the first leg to themandrel prior to forming the filament loops.
 33. The method of claim 15,further comprising securing the filament loops to the mandrel prior tobraiding the second leg.
 34. A method of fabricating a braided devicesuitable for implantation in an anatomical structure, the braided devicehaving a first leg, a second leg, a common body coupled to the first legand the second leg, and a hinge between the first leg and the secondleg, the method comprising: (a) securing a plurality of filaments to afirst tubular mandrel, the first tubular mandrel comprising a firstsegment and a detachable second segment, the two segments of the tubularmandrel having a common longitudinal axis, wherein said securing stepcomprising securing the filaments at a first location on the firstsegment of the first tubular mandrel; (b) braiding the plurality offilaments from the first location to a second location along thelongitudinal axis of the first segment of the first tubular mandrel toform the first leg; (c) securing the plurality of filaments to thetubular mandrel at the second location; (d) selecting a subset of theplurality of filaments proximal to the second location to form thehinge, each of the subset of filaments having a free end available forcontinued braiding along the longitudinal axis of the first tubularmandrel; (e) forming a loop in each of the remaining filaments of theplurality of filaments to form filament loops, each loop beginning andending proximal to the second location on the first tubular mandrel, andeach filament bearing a loop having a free end available for continuedbraiding along the longitudinal axis of the first tubular mandrel; (f)securing the beginning and ending of each filament loop to the firsttubular mandrel proximal to the second location; (g) braiding the freeends of the plurality of filaments, including both the hinge filamentsand the filaments bearing loops, from a first location to a secondlocation along the longitudinal axis of the second segment of the firsttubular mandrel to form the second leg; (h) securing the plurality offilaments to the detachable second segment of the first tubular mandrelat each end of the second leg; (i) detaching the second segment of thefirst tubular mandrel from the first segment and pivoting the secondsegment of the tubular mandrel about the hinge such that the twosegments of the first tubular mandrel are no longer in axial alignment;(j) positioning a second tubular mandrel proximal to the first andsecond segments of the first tubular mandrel for braiding of the commonbody; and (k) braiding either the filament loops, or wires formed bysevering the filament loops, along a longitudinal axis of the secondtubular mandrel to form the common body of the braided device.
 35. Themethod of claim 34, wherein the plurality of filaments are constructedof a shape memory metal, and the method further comprises the step ofheat treating the braided device to set the braided device into adesired final shape.
 36. The method of claim 35, wherein the shapememory metal is nitinol.
 37. The method of claim 34, wherein step (k)comprises braiding the filament loops to form the common body.
 38. Themethod of claim 34, wherein step (k) comprises severing the filamentloops into two severed wires, and braiding the severed wires to form thecommon body.
 39. The method of claim 34, wherein the subset of filamentsselected for the hinge represents about ⅛ to about ¼ of the plurality offilaments.
 40. The method of claim 34, wherein the number of filamentsin said plurality of filaments is from about 16 to about 72.